Cytoplasmic phospholipase A2 antagonists inhibit multiple endocytic membrane trafficking pathways.

Previous studies have suggested a role for cytosolic Ca(2+)-independent phospholipase A(2) (PLA(2)) activity in the formation of endosome membrane tubules that participate in the export of transferrin (Tf) and transferrin receptors (TfR) from sorting endosomes (SEs) and the endocytic recycling compartment (ERC). Here we show that the PLA(2) requirement is a general feature of endocytic trafficking. The reversible cytoplasmic PLA(2) antagonist ONO-RS-082 (ONO) produced a concentration-dependent, differential block in the endocytic recycling of both low-density lipoprotein receptor (LDLR) and TfRs, and in the degradative pathways of LDL and epidermal growth factor (EGF).

A block in endoplasmic reticulum-to-Golgi trafficking inhibits phospholipid synthesis and induces neutral lipid accumulation.

Seeking to better understand how membrane trafficking is coordinated with phospholipid synthesis in yeast, we investigated lipid synthesis in several Sec(-) temperature-sensitive mutants, including sec13-1. Upon shift of sec13-1 cells to the restrictive temperature of 37 degrees C, phospholipid synthesis decreased dramatically relative to the wild type control, whereas synthesis of neutral lipids, especially triacylglycerol (TAG), increased. When examined by fluorescence microscopy, the number of lipid droplets appeared to increase and formed aggregates in sec13-1 cells shifted to 37 degrees C.